Lift trucks are commonly used in warehouses, transfer yards, etc. for handling a variety of items. A large percentage of the items are loaded into containers or on pallets. The lift truck is fitted with forks that are maneuvered by the lift truck operator into receiving pockets provided in the containers or pallets. Controls enable the operator to raise the forks and its load which is then transferred as desired. (Hereafter references to pallets will be understood to be interchangeable with containers otherwise used for carrying or containing items which make up a load.)
Items have to be stored in the warehouse according to the ability of the lift truck to be maneuvered into position for picking up and then transporting the items. For example, aisles have to be wide enough for the lift truck to turn into a stack of loaded pallets. The loaded pallets can't be stacked higher than the reach of the truck, etc. Lift trucks that are compact in configuration with a short turning radius can be maneuvered in smaller spaces which is highly desirable. Also desirable from a maneuverability standpoint is the ability to side shift the forks relative to the lift truck. (This relates to the capability of the forks to be moved laterally relative to the lift truck.) With the side shift capability, a lift truck operator does not have to precisely align the lift truck with the pallet pockets. As he moves in to engage a loaded pallet, if the forks are not aligned with the pallet pockets, he simply engages the side shifting feature. Without this feature, the operator has to move the truck back and forth to obtain the correct alignment.
Prior to this invention, the side shifting feature was typically provided by a double carriage arrangement as follows: Uprights having limited tilting capability are mounted on the front of the truck. The uprights are provided with cooperative vertical guideways for slidably mounting a primary carriage that is raised and lowered relative to the uprights, e.g. by motor driven lifting chains. This primary carriage is designed to receive lifting forks as when the truck lift design does not require the side shift feature. The side shift feature is provided by a sliding carriage. This sliding carriage is similar to the primary carriage and is equipped with clamps that slidingly fit over an upper supporting edge of the primary carriage. Forks are mounted to the sliding carriage and the three desired fork movements are thus provided. The forks are raised and lowered by raising and lowering the primary carriage relative to the uprights. The forks are tilted by tilting the uprights relative to the truck. The forks are side shifted by moving the sliding carriage (via the sliding clamps) relative to the primary carriage.
In this prior device, the primary and sliding carriages are juxtaposed with the sliding clamps mounting the sliding carriage slightly forward of the primary carriage (made necessary by the clamps extended from the sliding carriage and reaching over the top edge of the primary carriage. In comparing the position of the forks mounted to the primary carriage versus their mounting to the sliding carriage, it will be appreciated that the forks on the sliding carriage are spaced substantially further forward from the lift truck. This forward mounting of the forks increases the "load moment arm" (the distance from the load to the center of the front wheels) which is an undesired characteristic of the prior side shift mounting.